I think this is a rather unfair, and possibly dangerous, attitude, to simply dismiss this phenomenon as typical young people "adventuring". Is it really adventuring if it's a decision made after countless hours of carefully weighing different employment options and coming to the conclusion that the US offers far more opportunities and far better rewards for our careers?
I have nothing but anecdotes to support that the brain drain is actually happening at any significant scale, but it's certainly not difficult to imagine why young people who are offered a US position would come to these same conclusions, given the sorry state of the Canadian tech industry today.
RE: Settling down. Seattle, which is a 3 hour drive from Vancouver, offers about double the average Vancouver salary with comparable housing prices. Needless to say, I'm not planning on going back until the situation improves dramatically.
This is what young people do; they adventure. Then, many times, they come back to their roots to settle down.
I'm sure there're a few people around these parts with anecdata regarding the joys of finding housing and raising a family in the SF Bay Area.